There are disk drive apparatus for recording information signals on and reproducing information signals from disk-shaped recording media. Such a disk drive apparatus has an optical pickup movable radially across a disk-shaped recording medium mounted on a disk table for applying a laser beam through an objective lens to the disk-shaped recording medium.
Some disk drive apparatus are capable of recording information signals on and reproducing information signals from disk-shaped recording media of different types, e.g., CD (compact disks) and DVD (digital versatile disks).
Such disk drive apparatus are required to emit two laser beams having different wavelength ranges from a light-emitting device because of different recording densities on CD and DVD. For the purpose of reducing the size of the optical pickup, a disk drive apparatus has an objective lens shared by two types of disk-shaped recording media and a light-emitting device comprising two light emitters disposed in one package for emitting respective two laser beams having different wavelength ranges. In such a disk drive apparatus, for example, the first light emitter emits a first laser beam having a wavelength of 650 nm to a DVD, and the second light emitter emits a second laser beam having a wavelength of 780 nm to a CD.
However, since the objective lens of the above disk drive apparatus is shared, the first light emitter and the second light emitter are disposed parallel to each other in a direction perpendicular to the optical axis of the objective lens. Therefore, though the optical axis of the laser beam emitted from one of the light emitters can be aligned with the optical axis of the objective lens, the optical axis of the laser beam emitted from the other light emitter has to be off the optical axis of the objective lens.
Since the optical axis of the laser beam emitted from either one of the light emitters needs to be off the optical axis of the objective lens, when the laser beam is emitted from the light emitter whose optical axis is off the optical axis of the objective lens, an amount of aberrations that are generated tends to be large, resulting in a reduction in the performance of the optical pickup thereby to cause a recording error and a reproduction error due to a signal level reduction or the like.
An optical pickup and a disk drive apparatus according to the present invention are aimed at overcoming the above problems and reducing an amount of aberrations generated for increased performance.